1. Field of the Invention
The present general inventive concept relates to a method and apparatus of dot counting, and more particularly, to a method and apparatus of dot counting with respect to each head chip of a group of head chips of an inkjet printer which includes a nozzle portion having a size corresponding to a width of a printing medium.
2. Description of the Related Art
An inkjet image forming apparatus may perform only a printing function, or may perform multiple functions combined with a copy machine, facsimile, and scanner. A non-impact type inkjet image forming apparatus produces less printing noise than a dot-matrix printer. In addition, the inkjet image forming apparatus can be light and compact, and a color ink cartridge may be used for color printing. Minute droplets of ink are discharged to a desired position on a printing medium by an inkjet head of the inkjet image forming apparatus. The inkjet head, which is included in a cartridge and is connected with an ink storage unit, is placed in the inkjet image forming apparatus. The inkjet head uses heat or piezoelectric elements as a driving source for discharging ink to provide a high resolution through semiconductor manufacturing processes, such as etching, deposition, and sputtering.
A nozzle portion of the inkjet head disperses the ink onto the printing medium. After printing, ink or foreign materials remain on a surface of the nozzle portion. The remaining ink or foreign materials can block holes of the nozzle portion over time, which can prevent a nozzle from dispersing ink droplets. In addition, a dispersion direction of an ink droplet dispersed by the nozzle may be changed, and an impact area of the ink droplet may be diverged. Thus, in order to maintain a clean surface of the nozzle portion of the inkjet image forming apparatus, a wiping element is provided for wiping the ink or foreign materials from the surface of the nozzle portion. Further, a spitting element is provided for removing foreign materials from the holes of the nozzle portion by dispersing ink in order to prevent the nozzle portion from clogging. Further, a capping element is provided for preventing the ink from drying and for protecting the nozzle portion from external foreign materials by covering the nozzle portion.
The wiping element, the spitting element, and the capping element are generally referred to as a maintenance element. An area of the inkjet image forming apparatus containing the maintenance element, where a maintenance operation is carried out, is referred to as a maintenance area. To miniaturize the inkjet image forming apparatus, the maintenance element must be miniaturized.
In a conventional inkjet image forming apparatus, ink is dispersed onto paper from an inkjet head (i.e., a shuttle type inkjet head) which reciprocates perpendicular to a feed direction of the paper (i.e., widthwise across the paper) to form an image. A nozzle portion of the inkjet image forming apparatus has a plurality of nozzles for discharging ink and is provided in the inkjet head. Instead of the shuttle type inkjet head, a line inkjet head, which includes a nozzle portion having a length corresponding to a width of a printing medium in a main scanning direction, has started to be used for high speed printing. Since the inkjet image forming apparatus having the line inkjet head has a fixed inkjet head and only the printing medium is transferred, high speed printing can be achieved with a simple driving element. For example, for A4 size paper, the length of the nozzle portion is approximately 210 mm, when a printing margin is not taken into consideration.
Conventionally, in order to carry out a maintenance operation of an inkjet printer having a plurality of head chips on an inkjet head, a number of ink droplets discharged from each inkjet head chip is counted, and the number of ink droplets counted until a printing medium (e.g., a sheet of paper) is completely printed is compared with a predetermined value. If the counted number of ink droplets exceeds the predetermined value, the maintenance operation (such as spitting, wiping, or capping) is carried out. In this method, the number of ink droplets discharged from each ink head chip in a printer carriage is counted to determine a service cycle for the plurality of head chips.
However, the conventional method has a problem in that an amount of dot printing for each nozzle of the plurality of head chips cannot be correctly estimated when using an inkjet head which includes a nozzle portion having a size corresponding to a width of a printing medium in a main scanning direction perpendicular to a feeding direction of the printing medium. In addition, since a nozzle usage is different for each head chip, it is hard to estimate when to start a maintenance operation.